Tone Generator and Probe - CT-NT041* The generator and probe is a patent prodcut, and domestic pioneer. * There are single and dual tone signal choices. * The LED shows the wire polarity, continuity and voltage, the current, polarity, bell and voltage of 568A/B(LAN)pairs or telephone net pairs. * It has the high sensitivity, with high volume, volume adjustable, vocal-light indication of result. * And it has the low-voltage warning function.